Preparation of highly active silica-supported Au catalysts for CO oxidation by a solution-based technique

Although Au catalysts can be readily prepared on titania via the deposition-precipitation (DP) method, the direct application of the method similar to the preparation of silica-supported Au catalysts only results in diminished success. This paper reports a novel, efficient method to synthesize highly active Au catalysts supported on mesoporous silica (SBA-15) through a gold cationic complex precursor [Au(en)2]3+ (en = ethylenediamine) via a wet chemical process. The gold cationic precursor was immobilized on negatively charged surfaces of silica by a unique DP method that makes use of the deprotonation reaction of ethylenediamine ligands. The resulting mesoporous catalyst has been demonstrated to be highly active for CO oxidation at room temperature and even below 273 K, the activity of which is much superior to that of silica-supported Au catalysts previously prepared by various solution techniques. The pH value of the gold precursor solution plays a key role in determining the catalytic activity through the regulation of [Au(en)2]3+ deprotonation reaction and the surface interaction of silica with the gold precursor. This mesoporous gold silica catalyst has also been shown to be highly resistant to sintering because of the stabilization of Au nanoparticles inside mesopores.     

Preparation of yttrium oxysulfide phosphor nanoparticles with infrared-to-green and -blue upconversion emission using an emulsion liquid membrane system

Yttrium oxysulfide upconverting phosphor nanoparticles, doped with Yb as a sensitizer and Er (or Ho, Tm) as an activator, have been prepared via a solid-gas reaction using precursor oxalate particles obtained in an emulsion liquid membrane (ELM, water-in-oil-in-water (W/O/W) emulsion) system. The resulting Y(2)O(2)S:Yb,Er particles, mainly smaller than 50 nm in diameter, demonstrated green upconversion emission under infrared excitation (lambdaex = 980 nm) via a two-photon process. Distinct green and blue upconversion emission were also demonstrated under the same infrared excitation from Y(2)O(2)S:Yb,Ho and Y(2)O(2)S:Yb,Tm nanoparticles, respectively. These upconverting phosphor nanoparticles, together with Y(2)O(3):Yb,Er infrared-to-red upconverting phosphor particles, with different emission under the same infrared excitation may be applied to the luminescent reporter materials for the detection of the targeted analyte in multiplexed assays.     

Study of CsCl incorporation in silica via sol-gel synthesis catalyzed by biogenic compounds

Incorporation of CsCl in silica via sol-gel route catalyzed by biogenic compounds with three different concentrations of CsCl has been carried out by using organic compounds extracted from Nitzschia spp., a freshwater diatom alga. The visual integrity, nitrogen adsorption and electron microscopies were used to characterize the silica gels obtained from the biocatalysts employing sol-gel process with tetraethylorthosilicate (TEOS) as precursor. The usual sequence for the sol-gel process was used: sol preparation, gelation, aging, drying and heat treatment. Differential thermal analysis (DTA), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to characterize the incorporation of CsCl in the biomimetic silica. Chemical analysis of the biocatalysts was used to explain the exothermic behavior of the samples during DTA and DSC. The incorporation of CsCl in the silica matrix with a process using biogenic catalysts proved to be more effective compared to another process using inorganic catalysts.     

Synthesis of novel magnetic nanoparticles with urea or urethane moieties: Applications as catalysts in the Strecker synthesis of α‐aminonitriles

Four novel magnetic nanoparticle catalysts with urea or urethane moieties are reported. The silica‐coated magnetic nanoparticles were simply functionalized via addition of 3‐(triethoxysilyl)propylisocyanate (TESPIC), amine or amino alcohol. TESPIC with dual labile functional groups was used as a suitable precursor for the synthesis of urethane‐based catalysts. The newly synthesized catalysts were fully characterized using a variety of techniques. These functionalized magnetic nanoparticles were used as reusable catalysts in the Strecker synthesis of α‐aminonitrile derivatives under solvent‐free conditions at 50 °C.     

Metal-free Knoevenagel condensation catalyzed by mesoporous and nitrogen-distribution-tunable supported carbon nitride

Research on Chemical Intermediates - A series of SBA-15 supported carbon nitride catalysts (CN/SBA15) were prepared via a facile impregnation method using dicyandiamide as a precursor, and then...     

过硫酸盐改性的Al2O3-ZrO2催化剂上的正丁烷异构化反应

The conversion of n-butane to isobutane over strong acid catalysts is an important process in the petrochemical refining industry, because isobutane is a valuable precursor to methyl-tert-butyl ether and other fuel additives. Many reports dealing with sulfate promoted zirconia as catalysts for n-butane isomerization have appeared[1, 2].     

Improvements in selectivity and stability of Rh catalysts modified by SnBu4. dehydrogenation of isobutane to isobutene

RhSn/SiO₂ bimetallic catalysts prepared via an organometallic route have proved to be very active and selective toward several hydrogenation reactions. In this work these catalysts were studied for the dehydrogenation of isobutane to isobutene. It was found that Rh/SiO₂ monometallic catalysts had a null selectivity to isobutene, and this selectivity increased up to more than 90% after the addition of tin, using SnBu₄ as precursor.     

The use of alumatrane for the preparation of high‐surface‐area nickel aluminate and its activity for CO oxidation

Supported nickel has been used in a wide range of applications for industrial reactions, such as steam reforming, hydrogenation and methanation. In this work, nickel aluminate was prepared by the sol–gel process using alumatrane as the alkoxide precursor, directly synthesized from the reaction of inexpensive and available compounds, aluminum hydroxide and TIS (triisopropanolamine) via the oxide one pot synthesis (OOPS) process. Various conditions of the sol–gel process, such as pH, calcination temperature, hydrolysis ratio and ratio of nickel to aluminum, were studied. All samples were characterized using FTIR, TGA, XRD, TPR, DR‐UV and BET. The BET surface area was in the range of 340–450 m²/g at the calcination temperature of 500 °C with a mesoporous pore size distribution. Catalyst activity testing in CO oxidation reaction depended on Ni:Al ratio and calcination temperature. Higher activity was obtained from higher Ni content and lower calcination temperature. In addition, catalysts prepared using alumatrane precursor had higher percentage conversion than those prepared using aluminum hydroxide precursor. Copyright © 2005 John Wiley & Sons, Ltd.     

Highly Stable Carbon-Shell Encapsulated Ni−Cu Bimetallic Catalysts for Efficient Conversion of Levulinic Acid to γ-Valerolactone

Non-noble Ni−Cu alloys serve as an alternative catalytic material for noble metal-based catalysts that could be applied in the efficient conversion of levulinic acid (LA) into the high value γ-valerolactone (GVL). However, maintaining the catalytic stability for Ni−Cu nanoparticles in the LA hydrogenation process remains a substantial challenge, Herein, this problem is solved by constructing carbon-protected catalytic sites within carbon layer-coated Ni−Cu nanoalloy composite via pyrolysis of NiCu_x(OH)/glucose precursor. The optimized NiCu_0.68@C catalyst exhibits excellent stability and selectivity to GVL (>99 %) in the hydrogenation of LA reaction. Various characterization indicates that the enhancement in stability originates from the protective effect of the carbon layer, which prevents the metal leaching, oxidation and aggregation of Ni−Cu nanoparticles during the reaction process. This work greatly advances non-noble metal-catalyzed conversion of LA to GVL and helps the rational design of bimetallic catalysts.     

采用相转移催化法制备苯二甲酰亚胺基甲基聚苯乙烯

以邻苯二甲酰亚胺钾盐为亲核取代试剂, 采用相转移催化体系通过Gabriel反应, 将氯甲基聚苯乙烯转变为苯二甲酰亚胺基甲基聚苯乙烯, 考察了各种因素对相转移催化反应的影响规律, 探讨了相转移催化机理. 结果表明, 采用相转移催化体系, 相转移催化剂将邻苯二甲酰亚胺负离子从水相中转移至油相, 与氯甲基聚苯乙烯发生亲核取代, 顺利地将氯甲基聚苯乙烯大分子链上的氯甲基转变成了甲基化的苯二甲酰亚胺基, 成功地实现了高分子的功能化转变. 影响相转移催化反应的主要因素有催化剂种类与用量、溶剂的极性、油相与水相比例及温度等. 当以十六烷基三甲基溴化铵为催化剂且以甲苯为有机相时, 反应效果最佳, 反应温度为50 ℃时, 反应8 h氯甲基的转化率可达到87%.     

Hydrogenolysis of n-butane on low-loaded Rh/TiO2, III. Selectivity studies

A study has been carried out on the selectivity of titania-supported rhodium catalysts in n-butane hydrogenolysis. It is concluded that incorporation of the rhodium precursor onto the titania surface via ion exchange leads to a less pronounced development of Strong Metal-Support Interactions and thus to an homogeneous distribution of active sites on the catalyst surface.     

非晶态配合物法制备钙钛矿型纳米粉体催化剂及其CO催化氧化性能

运用非晶态配合物法合成了LaCoO3,La0.9Sr0.1CoO3,LaCo0.3Mn0.7O3和 La2CuO4钙钛矿型纳米粉体催化剂，研究了其CO催化化活性及SO2中毒性能，初步推 断了中毒机理。结果表明用该方法可以在较低下合成具有纯钙钛矿结构的纳米粉体 催化剂，该催化剂具有很好的CO催化化活性，其中LaCoO3系列的催化活性优于 La2CuO4，所有催化剂经SO2中毒后催化活性均有所下降。研究表明钙钛矿结构的破 坏是硫中毒失活的主要原因。     

Multidisciplinary green approaches (ultrasonic,co-precipitation,hydrothermal, and microwave) for fabrication and characterization of Erbium-promoted Ni-Al2O3 catalyst for CO2 methanation

The dispersion of nickel catalysts is crucial for the catalytic ability of CO₂ methanation, which can be influenced by the fabrication method and the operation process of the catalysts. Therefore, a series of fabrication methods, including ultrasonic, hydrothermal, microwave, and co-precipitation, have been applied to prepare 25Ni-5Er-Al₂O₃ catalysts. The fabrication method can partially influence the structural and catalytic activity of the nickel aluminate catalysts. Among the catalysts modified by Erbium prepared with various methods, the catalyst fabricated by ultrasonic pathway exhibited better catalytic performance and CH₄ selectivity especially, at a temperature (400 ℃). The impact of the temperature of the reaction (200–500 °C) was examined under a stoichiometric precursor ratio of (H₂:CO₂) = 4: 1, atmospheric pressure, and space velocity (GHSV) of 25000 mL/gcath. The results demonstrate that the ultrasonic method is strongly efficient for fabricating Ni-based catalysts with a high BET surface area of about 190.33 m²g^?1. The catalyst composed via the ultrasonic technique has 69.38 % carbon dioxide conversion and 100 % methane selectivity at 400 °C for excellent catalytic performance in CO₂ methanation reactions. The fabrication effect can be associated with its high surface area, which is achieved via the hot spot mechanism. Besides, the addition of Erbium promotes the Ni dispersion on the supports and stimulates the positive reaction because of the erbium oxygen vacancies.     

Seedless growth of free-standing copper nanowires by chemical vapor deposition

Free-standing copper nanowires were synthesized by a chemical vapor deposition process at low substrate temperatures using Cu(etac)[P(OEt)3]2 as a precursor. The process requires neither templates nor catalysts to produce copper nanowires of 70-100 nm in diameter, which exhibited high purity and crystallinity with [111] orientation. The grain structures of the films deposited from a series of Cu(I) alkyl 3-oxobutanoate complexes indicated that the high precursor stability was responsible for the columnar growth of the grains, which was evolved to the nanowires eventually.     

Template-free sol–gel synthesis of high surface area mesoporous silica based catalysts for esterification of di-carboxylic acids

High surface area mesoporous silica based catalysts have been prepared by a simple hydrolysis/sol–gel process without using any organic template and hydrothermal treatment. A controlled hydrolysis of ethyl silicate-40, an industrial bulk chemical, as a silica precursor, resulted in the formation of very high surface area (719 m²/g) mesoporous (pore size 67 Å and pore volume 1.19 cc/g) silica. The formation of mesoporous silica has been correlated with the polymeric nature of the ethyl silicate-40 silica precursor which on hydrolysis and further condensation forms long chain silica species which hinders the formation of a close condensed structure thus creating larger pores resulting in the formation of high surface mesoporous silica. Ethyl silicate-40 was used further for preparing a solid acid catalyst by supporting molybdenum oxide nanoparticles on mesoporous silica by a simple hydrolysis sol–gel synthesis procedure. The catalysts showed very high acidity as determined by NH₃-TPD with the presence of Lewis as well as Brønsted acidity. These catalysts showed very high catalytic activity for esterification; a typical acid catalyzed organic transformation of various mono- and di-carboxylic acids with a range of alcohols. The in situ formed silicomolybdic acid heteropoly-anion species during the catalytic reactions were found to be catalytically active species for these reactions. Ethyl silicate-40, an industrial bulk silica precursor, has shown a good potential for its use as a silica precursor for the preparation of mesoporous silica based heterogeneous catalysts on a larger scale at a lower cost.     

Cooperative Bimetallic Catalysis via One-Metal/Two-Ligands: Mechanistic Insights of Polyfluoroarylation-Allylation of Diazo Compounds

Metal/ligand in situ assembly is crucial for tailoring the reactivity & selectivity in transition metal catalysis. Cooperative catalysis via a single metal/two ligands is still underdeveloped, since it is rather challenging to harness the distinct reactivity profiles of the species generated by self-assembly of a single metal precursor with a mixture of different ligands. Herein, we report a catalytic system composed of a single metal/two ligands for a three-component reaction of polyfluoroarene, α-diazo ester, and allylic electrophile, leading to highly efficient construction of densely functionalized quaternary carbon centers, that are otherwise hardly accessible. Mechanistic studies suggest this reaction follows a cooperative bimetallic pathway via two catalysts with distinct reactivity profiles, which are assembled in situ from a single metal precursor and two ligands and work in concert to escort the transformation.     

Easily accessible and highly tunable indolyl phosphine ligands for Suzuki-Miyaura coupling of aryl chlorides

This study describes a new class of easily accessible indolyl phosphine ligands, prepared via an efficient protocol involving Fischer indolization from readily available phenylhydrazine and substituted acetophenones. This versatile ligand scaffold provides beneficial features, including high potential of steric and electronic tunability. The air-stable indolyl phosphines in combination with a palladium metal precursor provide highly effective catalysts for Suzuki-Miyaura coupling of unactivated aryl chlorides, and the catalyst loading down to 0.02 mol % can be achieved.     

DFT Study on the Recovery of Hoveyda–Grubbs‐Type Catalyst Precursors in Enyne and Diene Ring‐Closing Metathesis

DFT (B3LYP‐D) calculations have been used to better understand the origin of the recovered Hoveyda–Grubbs derivative catalysts after ring‐closing diene or enyne metathesis reactions. For that, we have considered the activation process of five different Hoveyda–Grubbs precursors in the reaction with models of usual diene and enyne reactants as well as the potential precursor regeneration through the release/return mechanism. The results show that, regardless of the nature of the initial precursor, the activation process needs to overcome relatively high energy barriers, which is in agreement with a relatively slow process. The precursor regeneration process is in all cases exergonic and it presents low energy barriers, particularly when compared to those of the activation process. This indicates that the precursor regeneration should always be feasible, unlike the moderate recoveries sometimes observed experimentally, which suggests that other competitive processes that hinder recovery should take place. Indeed, calculations presented in this work show that the reactions between the more abundant olefinic products and the active carbenes usually require lower energy barriers than those that regenerate the initial precatalyst, which could prevent precursor regeneration. On the other hand, varying the precursor concentration with time obtained from the computed energy barriers shows that, under the reaction conditions, the precursor activation is incomplete, thereby suggesting that the origin of the recovered catalyst probably arises from incomplete precursor activation.     

Chemoselective sulfide oxidation mediated by bridged flavinium organocatalysts

The chemoselective oxidation of sulfides to sulfoxides, catalysed by bridged, tetracyclic flavinium catalysts is presented. The flavinium catalysts are easily prepared via a telescoped three-step process. A range of sulfoxides is accessed in excellent yield and chemoselectivity.     

活化条件对负载Ru催化剂的Ru粒子化学环境的影响

本文应用动态脉冲吸附技术测定了H_2和CO的吸附量,结合透射电镜(TEM)和程序升温还原(TPR)等表征技术考察了活化条件对金属Ru粒子化学环境的影响.发现活化条件对Ru催化剂H_2和CO吸附量的影响很显著,H_2和CO低温吸附量随焙烧温度的升高而锐减;改由在惰性气体中焙烧或载体经HCI或HF预处理,大大增加了低温吸附量.TEM测定结果表明:金属Ru平均粒径(?)值随焙烧温度(在623K以下的范围内)的升高而减小,说明在此活化条件下处理的催化剂,其低温H_2和CO化学吸附量不能反映金属的分散度.TPR结果说明在空气中焙烧催化剂,Ru非氧化物前身转变成为RuO_2,并且导致金属与载体之间产生较强的相互作用,改变金属Ru粒子的化学环境,吸附活化能垒增高,在低温下H_2和CO的吸附量很小.